Using unmanned surface vehicles for hydrographic surveying

Hydrographic survey is essential and widely welcomed in the world for economic, security and societal purposes. The question remains how to survey in a safer and faster way. One way to do this is by using unmanned surface vehicle (USV), a type of platform that can carry various kinds of sensors for hydrographic survey. This article discusses two applications of USVs.

Fig. 1a and 1b: Traditional hydrographic survey.

Water is a basic resource for all living creatures. Even in ancient civilisation you will find references made to water bodies that support societies. Today, more than 95% of city, towns and villages are established near rivers, brooks and wells. From the 19th to the 21st century, industrial revolutions have further established the relationship between humans and water with more bridges, ports and harbour being built for economic and social purposes.

Hydrographic surveying using technologies such as multi-beam echo sounders, side scan sonars, sub-bottom profilers and even lidar for topographic and hydrographic purposes, have come to play a key role in these processes.

Traditionally, hydrographic surveys required surveyors to find and rent boats, install echo sounder and other accessories, and determine the best position to mount the transducer to minimise interference from waves and the boat’s propellers. Using boats, surveyors also had to take the depth of the water into account, and shallow waters could pose a risk of being stranded. To avoid being stranded, some surveyors resort to using bamboo or other small rafts/crafts, but these pose safety risks like capsizing, lack the proper facilities to conduct surveys, and cannot operate in environments such as the ocean or tailing dams.

Besides safety concerns, administrative authorities and the surveyors that help execute projects face challenges around time and speed of a project, often associated with the rate of urbanisation, as well as challenges around accuracy and efficiency.

Fig. 2: Pearl River Delta, intertwined within the water network.

Projects in China which employ USVs provide some examples of possible solutions to the above challenges.

Traffic channel survey

Pearl River Delta, intertwined in a wide water network, has become one of the most important economic engines for an industrial area in China since 1979. More than 30% of goods made in China are produced or assembled along this area and exported to the rest of the world from there. The water network with its hundreds of harbours have been playing an important role in goods export and raw material import. There were plans to build more pipelines for electricity, gas and municipal water across some channels. Before laying the pipelines, the constructor must survey the channels to understand the water bed. One of the main channels that the pipelines will be crossing is called the Modao Gate Channel. It is 89,5 km long, flows past more than 30 ports and thousands of factories, and has brought eight hundred 3000-tonne vessels to the channel.

The surveyors were tasked to conduct a hydrographic survey within 20 cm accuracy for five channels that the pipelines were going to pass through. With heavy traffic on channel (and without a traffic light to control it), it would be unsafe for the surveyors to sail a boat or ship across the river to do the cross-section survey.

Fig. 3: The iBoat BM1 unmanned surface vehicle system.

Besides the safety concerns and the risk of causing accidents, a cross section survey using a traditional boat could slow down or delay the traffic on the channel. The shallow areas of the channels pose a further challenge to using a traditional hydrographic survey by boat, as does the high cost of conducting such surveys periodically.

Employing a USV system

Using a USV solution assisted the surveyors in finishing their work on time and mitigating risks to their safety.

Fig. 4: The planning of survey lanes backgrounded in the USV’s software.

They used an iBoat BM1 USV, which has the ability to operate for twelve hours continuously. This USV is an advanced and autonomous system which comprises a vessel body, echo sounding module and positioning module, a data communication system and a control system. Its auto pilot function aides the precision of the survey, as the gap between each survey lane can be preciously implemented (within 10 cm offset). Similar to unmanned aerial vehicles, the craft automatically returns to any of a number of pre-set home points when it loses signal or when the battery is insufficient for conducting the mission it has been tasked with. The real-time video transmission can also help surveyors monitor the craft from the river bank.

Fig. 5: Data can be transmitted from the boat to the laptop.

The project planning entailed first designing the survey lanes on an online Google Maps satellite image backdrop within the USV pilot software. The interval and length of each cross-section lane can be specified. Once the survey lanes have been set up, the USV can be navigated along them automatically or manually, with the operator able to switch the working mode in real-time. The manual navigation function was useful in this project as it allowed the operator to navigate and avoid the heavy ships. The craft’s light weight makes it flexible and swift to respond.

The survey can be monitored in real-time with the data being transmitted form the boat to the laptop software, allowing the operator to monitor the position, heading, depth and control other parameters for the sounding system remotely.

River monitoring

Fig. 6: Results from the survey.

The Hun River, often called the “Mother River,” is not deep enough to carry large cargo ships, but it is important to the Shenyang City, the capital of Liaoning Province, for municipal water supply. This river surrounds the city like a belt. The Water Resource Authority of Shenyang City needs to monitor the hydrographic conditions yearly and monthly for civil security, waterfront maintenance and sustainable development studies. The monitoring required a hydrographic survey with 20 m section intervals for an 80 km survey length (i.e. up to 1000 km surveying lanes), to be conducted within a month.

Fig. 7: The iBoat USV.

Several dams and hidden shoals in the river make the logistics and transport of a traditional hydrographic survey boat difficult and unsafe. For these reasons Shenyang City decided to use a USV for hydrographic monitoring. The iBoat BM1 USV made it possible to complete the job within 14 days.

Conclusion

Unmanned surface vehicles are smart platforms that can help surveyors improve the safety and efficiency of hydrographic survey projects. Their lightweight designs and autonomous systems make them well suited to and widely used in hydrographic surveys of rivers, channels, shallow water, lakes and reservoir.